Disk drives comprise a disk and a head connected to a distal end of an actuator arm which is rotated about a pivot by a voice coil motor (VCM) to position the head radially over the disk. The disk comprises a plurality of radially spaced, concentric tracks for recording user data sectors and embedded servo sectors. The embedded servo sectors comprise head positioning information (e.g., a track address) which is read by the head and processed by a servo controller to control the velocity of the actuator arm as it seeks from track to track.
FIG. 1 shows a prior art format of a disk 2 comprising a plurality of concentric servo tracks 4 defined by embedded servo sectors 60-6N. A plurality of data tracks are defined relative to the servo tracks 4, wherein the density of the data tracks may be different (e.g., higher) than the servo tracks 4. Each servo sector (e.g., servo sector 64) comprises a preamble 8 for synchronizing gain control and timing recovery, a sync mark 10 for synchronizing to a data field 12 comprising the coarse head positioning information (such as a Gray coded track ID), and servo bursts 14 which provide fine head positioning information. The head is positioned relative to the servo tracks 4 in order to position the head over a target data track.
The ability of the disk drive to accurately recover data recorded on the disk is affected by the fly height of the head during both write and read operations. Accordingly, disk drives typically employ a suitable fly height actuator (e.g., a heater or a piezoelectric actuator) for dynamically controlling the fly height of the head during write/read operations. The fly height actuator typically comprises a digital-to-analog converter (DAC) that is programmed with a digital value corresponding to a target fly height.